Consistently use implements when one interface inherits from another interface

pkg/analysis_server/lib/plugin/protocol/protocol.dart

Index: pkg/analysis_server/lib/plugin/protocol/protocol.dart
diff --git a/pkg/analysis_server/lib/plugin/protocol/protocol.dart b/pkg/analysis_server/lib/plugin/protocol/protocol.dart
index 823ffd61dc1e33dbccdfc598be5a44d8de2afc55..2e339577a8e2cf305f2d2679862c062f425195d2 100644
--- a/pkg/analysis_server/lib/plugin/protocol/protocol.dart
+++ b/pkg/analysis_server/lib/plugin/protocol/protocol.dart
@@ -20,7 +20,7 @@ part 'generated_protocol.dart';
  *
  * Clients may not extend, implement or mix-in this class.
  */
-abstract class DomainHandler extends RequestHandler {
+abstract class DomainHandler implements RequestHandler {
   /**
    * Perform any operations associated with the shutdown of the domain. It is
    * not guaranteed that this method will be called. If it is, it will be